Heat transfer and refrigeration



July 31, 1934. T. MlDGLEY, JR., Al. 1,968,049

HEAT TRANSFER AND REFRIGERATION Original Filed Feb. 8, 1930 mensa s1,1934 y 1.96am HEAT TRANSFER AND BEFBIGEEYATION Thomas Midgley, Jr.,Worthington, Albert L. Henne, Columbus, and Robert B. McNary,

Dayton, Ohio, assignors, by meine assignments, to General MotorsCorporation, a corporation of Delaware Original application February 8,1930, Serial No. 426,974. Divided and this application November 19,1931, Serial No. 576,052

2 Claims.

This applicationrelates to' the art of transferringV heat from one pointto another and specifically to the art of refrigeration, and is adivision of application Serial No. 426,974, now

5 Patent No. 1,833,847, granted November 24, 1931.

Heretofore, as far as we are aware, refrigerants and heat transferagents have been chosen chieily'for their boiling points and stabilityin the refrigerating or heat transfer cycle irrespective of otherdesirable'properties, such as noninammability and non-toxicity.

It is the object of our invention, on the other hand, to provide aprocess of refrigeration and, generically, a process of heat transfer inwhich these desirable properties, such as non-inflammability andnon-toxicity, are obtained in combination with the desired boilingpoints.

Broadly stated, the part of our process which deals With thecontrolling'of the properties of the refrigerating or heat transferagents consists in replacing hydrogen by fluorine or other halogen, orboth, in aliphatic hydrocarbons in which at least one hydrogen hasalready been replaced by uorine.

' Broadly stated, the part of our process which relates to the transferof heat or the production of refrigeration comprises changing thephysical state of, for example, by condensing or evaporating, ahalo-nuoro derivative of an aliphatic hydrocarbon, and dissipating to,or withdrawing from, anV object to Abe heated or cooled, the latent heatnecessary for changing the physical state of the said derivative. By ahalouoro derivative of an aliphatic hydrocarbon We mean a derivativecontaining more than one uorine atom withor without other halogen atoms,or one fluorine atom with onev or more other halogen atoms.

Referringnow specically to our mode of con- 4()A trolling4 theproperties of the refrigerating or heat transfer agent, aliphaticmonouorides form the structural nucleus on which the agents are built.Broadly speaking, if in the structural formula CHaF we increase thefluorine content (number of atoms) by the substitution of fluorine forhydrogen, stability increases, inammability decreases, and toxicitydecreases. 1f we keep the uorine content constant and substitute anotherhalogen for hydrogen in the 50,nucleus, the boiling point increases, thestability decreases, the toxicity increases, and the inflammabilitydecreases. 'I'he degree to which these variations take place depends onwhat the other halogen (chlorine, bromine, or iodine) 5511s;v As theratio of the halogen content to the hydrogen content increases theinflammability decreases.

Because there are several variables, and because of the value ofrelative proportions, we

'have'placed the compounds of the group just 60,

discussed on plots wherein Fig. 1 is a plot applying the rules ofsubstitution to typical groups having one carbon atom, and

Fig. 2 is a plot applying the rules to groups 65 having -two carbonatoms.

Fig. 3 is a key to Fig. 2, showing the radicals corresponding to thenumbers used in Fig. 2.

Referring to the plots generally, the dashed lines indicate iluorinesubstitutions and the solid lines indicate chlorine substitutions.Similar plots are obtained with bromine and iodinerin place of chlorineexcept that the plot is elongated in the direction of highertemperatures with bromine, While with iodine the temperatures are stillmore elevated. The amount of elongation is readily determined byapplying the boiling points of some of these compounds.

Referring specifically to Fig. 1, this plot contains all the compoundswhich can be derived 30 from CHsF by chlorine and/or uorinesubstitutions, together with data which assist in the `formation of theplot. On the base line appear the numerals zero to four which showhalogen content, and the vertical line gives the approxg5 imate boilingpoints in degrees centigrade. At each point of intersection is given-the chlorine and uorine content and the complete formula of thecorresponding compound isfound by making this halogen substitution forhydrogen in the formula CH-r. We have drawn a horizontal dashed line atabout 25 centigrade to indicate approximately the optimum vapor pressureconditions which we desire for operating an air cooled refrigerator. Itis obvious that one may deviate more or less from this line to obtainoptimum conditions which include some other factors, so that within theneighborhood of this line we can provide a suitable refrigerant to meeta wide variation in limitations imposed. If under other refrigeratingconditions another optimum line is found desirable, the same choice maybe p made in the neighborhood of that line. In fact,

the actual operation of the refrigerator and the providing of thecharacteristics of the refrigerant are here combined as one problem soas to obtain the most desirable process of refrigeration under a givenset of conditions.

` In Fig. 2 we have shown the same mode of controlling the properties ofa refrigerant carried to compounds of the same type as in Fig. 1 buthaving two carbon atoms. The key to the chart is given in Fig. 3. Forexample, compound 9.1 is CH3.CH2F, compound 2.9 is CHF2-CC12F, compound1.4 is CHzECHClz. and compound 2.2 is CHF2.CHF2.

When we choose as our nucleus a compound having two or more carbon atomswe find that the structural formula gives a choice as to where thesubstitutions of the halogens shall be made. For example, the structuralformula of CaHsF is CHs--CHzF which has4 a boiling point at about 32 C.If we make a iluorine substitution for hydrogen in the second radical ofthis structural formula so that it reads CHa-CHFz we have arefrigerating agent whose boiling point is about --26 C. If we make thefluorine substitution for hydrogen onto the other carbon atom so thatthe formula reads CHzF-CHzF the boiling point of thisrefrigerant isabout 5 C. Thus, the rst type of substitution yields a compound boilingsubstantially lower than the compound obtained by the second type ofsubstitution, and the chart shows this to be general. The substitutionof chlorine, bromine or iodine for hydrogen raises the boiling point,but the substitution in a radical which does not already contain ahalogen raises the boiling point more than when the substitution is madein a radical which already contains a halogen.

The plot may be expanded in like manner Vwith other aliphaticmono-iluorides. As the number of carbon atoms increases the complexityand extent of the plot will increase together with .the number ofhalogens present. `These halogen derivatives of aliphatic mono-fluoridesmay be represented by the formula CnHmFpXr in which C represents carbonand n the number of carbon atoms in the molecule which is always equalto one or more.

H represents hydrogen and m the number of atoms thereof, which may equalzero and still fulll the'requirements of our invention.

F represents uorine and p the number of atoms thereof which is alwaysequal to one or more.

X represents chlorine, bromine or iodine or combinations thereof and rthe total number of such atoms. r may be zero when p is greater thanone.

Among the chemical groups that these refrigerants fall in are halogenderivatives of aliphatic mono-fluorides, halogen derivatives of alkylmono-fiuorides, aliphatic fluoro halides, alkyl iiuoro halides, uoroderivatives of methyl fluoride, fiuoro-halo derivatives of methane andfluoro chloro derivatives of methane.

Thus by our mode of making nuorine and/or other halogen substitution ina monoiiuoride, we can meet any conditions of refrigeration and provideour refrigerant with the desired properties, such as non-toxicity andnon-inflammability, along with such properties as stability and properboiling points.

Referring more specifically to the part of our process which relates tothe actual transfer of heat, We accomplish this transfer of heat bychanging the physical state of, for example, condensing or evaporatingour aliphatic hydrocarbon derivative which contains more thanA oneluorine atom with or without other halogen atoms, or one fiuorine atomwith one or more other halogen atoms, and by dissipating to orwithdrawing from an object to be heated or cooled, the latent heatnecessary for the change in physical state. More specifically, toproduce refrigeration, we may evaporate the desired derivative in thevicinity of a body to be cooled, while if a heating effect is desired,we may condense the derivative in the vicinity of a body to be heated,it being understood, of course, that the terms evaporation andcondensation include the separation of a gas from, and the absorption ofa gas in, an absorbent respectively.

Our invention Will probably nd its greatest utility by adjusting boththe mode of preparing the refrigerant to obtain desirablecharacteristics and the mode of using the refrigerant to obtain aprocess of refrigeration or heat transfer which meets the limitationsimposed. We prefer to employ refrigerants boiling above h60" C.

Obviously our invention is not limited in its application to anyspecific form of apparatus for carrying out the mode of operationdescribed and it will not be Anecessary for a complete understanding ofthe invention to show a specific embodiment of apparatus. Nor is thepresent invention limited to the examples set forth, for a particularadvance of the present invention resides in the fact that a great numberof new refrigerants with graduated properties is rendered available, andthat one is accordingly enabled to secure the most suitable refrigerantfor varied purposes.

What is claimed is as follows:

1. The method of transferring heat which comprises condensing andsubsequently evaporating CHzClF.

2. The method of producing refrigerationy which comprises evaporating inthe vicinity of a body to be cooled and subsequently condensing C HzClF.Y

ALBERT L. HENNE. THOMAS MIDGLEY, JR. ROBERT R. MCNARY.

